As smartphones have become dominant in the cellular marketplace, companies are selling increasingly sophisticated wireless accessories. These accessories, such as headphones, wristwatches, glasses, and other wearable devices, are designed to connect to smartphones or other accessories in a secure manner. The devices communicate with one another using one or more well-known methods such as Bluetooth® or one of the IEEE 802.11 standards.
During communication between the accessory and the smartphone, it is generally desirable to keep the received signal strength (as perceived by each device) within a particular power range, sometimes referred to as the Golden Receive Power Range or Golden Window. The upper and lower boundaries of this range vary, but in one implementation this range is from −60 dBm to −40 dBm. To do so, devices can issue power control commands to one another to indicate whether their transmit power should be increased or decreased.
In some architectures, such as Bluetooth®, power control is open loop in that when one device tells another device to change its transmit power, the device making the change does not provide feedback as to what its transmit power really is. Furthermore, the device making the change does not necessarily do so in equally-sized power steps, but instead makes the changes within a certain range.
Many wireless communication schemes employ a split host-controller architecture, in which a host processor (typically an Applications Processor (“AP”)) performs the more sophisticated, power-intensive tasks while a radio controller handles the physical communication and the low-level tasks related to the radio link. It is possible that the AP and the radio controller are integrated into the same hardware package, but even then there may be a logical separation between the two.
This split architecture can be exploited to minimize power consumption. To do so, a system designer tries to push as many tasks as possible down to the radio controller. There are limits on how much this can be done, however. In some cases, the limitations are a consequence of the capability of the radio controller. Radio controllers tend to have less processing power than host processors and are therefore less able to perform certain calculations, such as those involving floating point numbers. Furthermore, radio controllers generally operate at a lower layer in the Open System Interconnection (“OSI”) sense and are thus prevented from performing certain tasks.